Bonding Effects in Metal Complexes

Although the existence of Jt-bonding in some metal complexes has been accepted for more than 30 years, there have been doubts in certain cases and the subject remains controversial. 

The resultant of aU the influences on n (and o) bonding is generally reflected in the large variations in metal-phosphorus bond lengths which are observed in different complexes with the same metal atom, and sometimes with the same phosphine group. 

When the observed metal-phosphorus bond loigth is substantially less than the conventional (single) bond radium sum, it has been a general practice to assume that some degree of Ji-bonding is probably present, but this is by no means certain. If present, the Jt-bonding may not be wholly of the 3dJt(P)-dJt(M) type and 3p orbitals could sometimes be involved. 

On the basis of IR stretching frequencies, NMR and other data (Chapter 14.2), the order of Jt-acceptor capacity has been suggested as  

TABLE 8.18 Observed Ranges of Metal-Phosphorus Bond Lengths (A)  

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